Risk of flooding in area high

The risk of spring flooding in southeastern Minnesota is above to well-above normal, according to the National Weather Service office in La Crosse.

In Fillmore County and most of Houston County, the risk of minor flooding is greater than 50 percent. In Houston County adjacent to the Mississippi River, the risk is greater than 50 percent for major flooding, which is the case the length of the Mississippi south of Minneapolis through the state.

The forecast by the NWS is based on current conditions along with expectations based on climatology. The speed at which snow melts and the amount of precipitation will have a big impact on the severity of any flooding this spring and will need to be monitored on a week-by-week basis through March and April, reports the service.

 Primary driving factors for this outlook, according to the NWS, include:

• Heavy precipitation: There have been well above normal precipitation during the fall and winter months across much of the region, with the highest anomalies centered across this area.

• Wet soils:  The ground is near the 99th percentile for early March, combined with persistent higher than normal flows through the winter, especially along the Mississippi (nowhere for the water to go). This means that any rain or melted snow that occurs will run off quickly this spring.

• Ice cover: There is well above normal amount of ice cover on rivers, which has already been broken up once and re-frozen in place. This added ice could increase the risk for larger ice jam formation and added flooding risk.

• Expansive snow pack: The entire region is covered by well above normal snow pack, with snow water equivalent values of two to four inches common, highest in the headwaters of the Mississippi. The snow pack is near the top of climatology for early March, meaning not many years have been higher than this one for snow on the ground.

• Frozen ground: The frost depth is 18 to 30 inches, though this is more related to run-off potential if the area should get heavy rainfall.

• Lack of reservoir capacity: Some reservoirs are already near capacity due to persistent higher flows this winter. There is not as much room to hold back water as compared to recent years.

There are unknown factors at the time of this assessment on March 7 that could change the outlook. A slower, steady melt would mean a gradual run off of the water in the snow and would reduce the flooding risk. A rapid warmup would mean the opposite.

Trends as of March 7 support wet conditions (both rain and snow) through mid-March. There is some potential for drier than normal conditions to develop by late month, the service forecasts, although it also cautions that it only takes one big rainfall and warm-up to cause problems.